Steerable vehicle

ABSTRACT

A steerable, self-propelled vehicle ( 20 ) includes a rotatable steering column that is connected to control the steering angle of one or more ground-engaging members of the vehicle. The vehicle includes between the steering column and the ground-engaging member a first steering servomechanism having at least a first steering assistance characteristic; a second steering servomechanism having a second steering assistance characteristic also being connected to act on the steering column. A controller is provided for causing the first and second steering assistance characteristics to influence the steering of the vehicle in dependence on one or more one or more control commands generated in the controller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage filing of InternationalApplication Serial No. PCT/EP2012/067082, entitled “A STEERABLE VEHICLE”filed Sep. 3, 2012, which claims priority to Italian Application SerialNo. TO2011A000795, filed Sep. 7, 2011, each of which is incorporated byreference herein in its entirety for all purposes.

FIELD OF THE INVENTION

This invention relates to a steerable, preferably driver-operated,self-propelled vehicle. In particular the invention relates to arelatively heavy vehicle that is required to perform differingmanoeuvres on a variety of types of surface. The invention therefore isapplicable e.g. to construction vehicles such as excavators, bulldozersand backhoe loaders; certain classes of military vehicle; andagricultural vehicles such as tractors, in respect of which theinvention is most strongly applicable; farm loaders/grabs; andmultipurpose vehicles (i.e. a pick-up-type vehicle having a forward cab,a pick-up deck, a four wheel drive powertrain equipped with off-roadtyres and a low ratio transfer box permitting the towing of agriculturalimplements).

BACKGROUND OF THE INVENTION

It is well known to provide power assistance to the steering sub-systemsof driver-operated vehicles.

In various types of vehicle it has for many years been commonplace,especially in the case of relatively large vehicles in which therequired steering effort may be significant, to provide power assistancein the form of a hydraulic servomechanism. This includes a pump forpressurising a fluid such as hydraulic oil in a circuit that includes aservovalve. The degree of opening of the servovalve is determined byturning of the steering column, of the vehicle, that is coupled to aninput shaft of the valve by way of a mechanical linkage.

The valve pilots the hydraulic fluid pressure, in dependence on theresulting valve setting, to an assist motor that in some applications isa linear hydraulic cylinder having at each end an extensible arm and insome other applications may be e.g. a hydrostatic motor.

The cylinder when fitted interconnects by way of the ends of the armsthe steerable wheels of the vehicle in replacement of conventional,solid steering linkage members. The cylinder may act in the same manneras the rigid linkages or, when extension of the arms occurs as a resultof operation of the servomechanism, to reduce the effort needed to turnthe steering wheel against the resistance provided by the mass of thevehicle acting through the steerable wheels.

Power assistance of this general kind renders the feeling of thesteering “light” (i.e. relatively effortless) as experienced by thedriver of a vehicle equipped with it. Moreover if the servomechanismfails for any reason the cylinder becomes rigid and behaves in the samemanner as a conventional linkage member. In consequence it remainspossible to steer the vehicle, albeit through the application ofconsiderably more effort on the part of the driver, in the event of aservomechanism fault developing.

One characteristic of hydraulic servomechanisms of the general kinddescribed above however is that they do not on their own provide a“self-centring” characteristic. This is of course important in mostself-propelled, driver-controlled vehicles since it is stronglydesirable that the steerable wheels return to a “straight ahead” settingin the event of the driver releasing a steering input member (that in apassenger car and the majority of the vehicle types listed is a steeringwheel).

Passenger vehicle steering is normally designed to incorporate apositive caster angle that gives rise to a mechanical self-centringeffect. This tends to provide directional stability when the vehicle isdriven on relatively smooth, metalled roads as is normally the case forsuch a vehicle.

A self-centring steering effect is of limited benefit in the case ofagricultural vehicles when they are operating in off-road situationssuch as when driving in fields.

This is partly because furrows or other features of e.g. a ploughedfield tend to override any self-centring effect brought about throughdesign features including positive camber angles. The forces induced bythe furrows on the steerable wheels (or other ground-engaging members ofthe tractor, if fitted) exceed any self-centring forces induced by thesteering geometry.

Moreover under many circumstances when operating in a field a tractoroperator may find a self-centring effect to be inconvenient. Examplesarise when turning at a headland, or when following a curved margin of afield, when driving on lateral slopes (in a so-called “crab-likemotion”), or when ploughing with two wheels in a furrow.

At such times it may be desirable in effect to “set” a steering anglefor an extended period of operation. The tractor driver therefore mayfind it bothersome to have to adjust the steering input membercontinuously in order to overcome a self-centring effect and assureconstancy of the steering angle.

In any event a modern tractor is a complicated multi-purpose vehiclethat may be fitted with or coupled to numerous sub-systems (such asharvesters, spraying equipment and tilling implements) that requireoperation from within the operator's cab. When operating suchsub-systems the driver may find it very difficult simultaneously to makesteering input adjustments.

On the other hand when moving in a straight line on a relatively flatfield, or when driving on roads, a tractor operator may find itdesirable for the tractor to behave in ways that are similar to otherroad vehicles, and thereby exhibit a self-centring steering effect orother effects that are useful from the standpoints of safety, stabilityand/or convenience.

Another known type of power steering assistance mechanism is an electrictype, in which rotations of the steering column are converted (e.g.using a Hall effect device, or another kind of sensor) into electricalsignals. These in turn may be used to generate commands for an electricmotor that is connected to provide rotational assistance forces to thesteering column. Indeed in some arrangements the shaft of the steeringcolumn itself is constituted over part of its length as the rotor of themotor.

It would be desirable to be able to adjust the characteristics of thesteering of a large, heavy vehicle that operates under varyingcircumstances, to take account of the prevailing type of use. Thepresence or absence of a self-centring steering effect is exemplary ofthe kind of characteristic it could be desirable to adjust, althoughthere exist others such as but not limited to the degree of damping ofthe steering (i.e. the extent to which the steering deviates from a setsteering angle); the extent to which power assistance applies to assistthe vehicle operator; assistance in turning from one lock to theopposite lock as quickly as possible; and more general transitions ofcharacteristics that take account of changes from rough off-road toon-road or smooth field driving.

SUMMARY OF THE INVENTION

The invention seeks to provide one or more advantages not available inexisting power steering assistance. To this end according to theinvention in a broad aspect there is provided a steerable,self-propelled vehicle including a steering mechanism having a rotatablesteering column that is connected to control the steering angle of oneor more ground-engaging members of the vehicle, the vehicle includingacting on the steering mechanism at a first location (e.g. at an end ofthe steering column and lying between the steering column and theground-engaging member) a first steering servomechanism having at leasta first steering assistance characteristic; acting on the steeringmechanism at a second location, e.g. part-way along its length a secondsteering servomechanism having a second steering assistancecharacteristic; and a controller for causing the first and secondsteering assistance characteristics to influence the steering of thevehicle in dependence on one or more driver inputs and/or one or morecontrol commands generated in the controller.

The presence of two servomechanisms having differing assistancecharacteristics, together with a controller for determining the extentto which each of them confers its assistance characteristic(s) on thesteering of the vehicle, means that it is possible to provide a widevariety of steering modes in the vehicle. These may be designed forexample for when travelling in a ploughed field or on rutted ground, orfor when travelling on smoother surfaces. A variety of othercharacteristic choice criteria may equally well form the basis for adesign/control philosophy based on the invention as broadly stated.

By “connected” herein is meant a variety of ways of causing orpermitting one component or sub-system to influence another. Thus forexample the steering column may be connected to control the steeringangle of the one or more ground-engaging members by way of a physical(mechanical) connection or an electronic connection involvingservomotors and signal wires or wireless communication protocols.Another possibility is for the connection to be by way of fluid powercomponents such as hydraulic or pneumatic circuits.

In preferred embodiments of the invention the vehicle isdriver-operated, but as explained below this need not necessarily be thecase.

Preferably the first steering servomechanism is a hydraulic steeringservomechanism including a hydraulic steering valve that generates apilot hydraulic signal in relation to the rotational angle of thesteering column and at least one hydraulic steering cylinder connectedto adjust the steering angle of the one or more ground-engaging members,the pilot hydraulic signal being piloted to control the hydraulicsteering cylinder.

The first steering servomechanism therefore may in preferred embodimentsof the invention be similar to known hydraulic power steering systems ofthe kind described above. Indeed it is possible within the scope of theinvention to adapt known power steering hydraulic systems at low costfor use as the first servomechanism of the invention. In otherembodiments of the invention however the first servomechanism may be ofother designs.

Also preferably the second steering servomechanism is an electric powersteering servomechanism including a motor for generating a torque(rotational force) that acts on the steering column; and a signalgenerator for generating control signals determining the magnitude anddirection of action of the torque.

The use of an electric power steering servomechanism means that it isreadily possible to provide, in the vehicle of the invention, a hybridsteering assistance arrangement in which the two servomechanisms havediffering, yet readily combined, characteristics.

In like manner to the first servomechanism the second servomechanism maybe of the kind described above, or may of another type as desired anddepending on the precise application under consideration.

Conveniently the controller is programmable and the vehicle includes ahuman-machine interface (HMI) using which a driver may input commandsselecting two or more programmed modes of operation of the steeringservomechanism.

The HMI may be designed to provide for ease, and speed, of use, therebyminimising the extent to which a tractor driver must pay attention tothe selection of steering assistance modes while performing difficultmanoeuvres. To this end when the vehicle is an agricultural vehicle theHMI includes switching interfaces for selecting between programmed modesthat control steering during movement of the tractor respectively in afield headland and in other locations.

Preferably the HMI includes respective switches for selecting theprogrammed modes and sequentially selecting sub-modes followingselection of a said programmed mode. Thus in preferred embodiments ofthe invention the HMI may permit “scrolling” through a sequence ofselectable modes in a manner that is extremely simple to achieve andthat can be completed quickly.

Optionally and preferably the other locations include but are notlimited to fields and roads.

In particularly preferred embodiments of the invention the sub-modesavailable following selection of headland operation include a dampedsteering sub-mode, a maximal assistance (“effortless”) sub-mode,automatic steering centring sub-mode and a lock-to-lock assistancesub-mode as defined herein; and the sub-modes available followingselection of other location operation include an on-road sub-mode, adamped steering sub-mode and a maximal assistance (“effortless”)sub-mode as defined herein.

Conveniently the vehicle includes two or more selectively operablesteering input members connected to the steering mechanism that are orinclude a steering wheel and a joystick. The invention therefore issuitable for use in an agricultural tractor or backhoe loader in which ajoystick control is provided for the purpose of permitting a driver tosteer the tractor when his seat is reversed and he/she is viewingoperations of the vehicle via a rearwardly facing window of the operatorcabin.

When present the steering wheel preferably is mechanically coupled tothe steering column, although it is possible for the steering wheel tobe an electronic input device that generates electrical signals insteadof being directly physically coupled to the steering column. Thejoystick preferably is electronically coupled to the second steeringservomechanism, although in certain embodiments of the invention it maybe connected by way of a pneumatic or hydraulic movement mimic circuit,or even a mechanical linkage.

Although conventionally the phrase “steering column” refers to anelongate, shaft-like column that is rigid in normal use and extends fromthe forward bulkhead of the vehicle cab to connect to forwardly mountedsteering linkage components, this need not necessarily be so in the caseof the invention. Thus the steering system of the vehicle may operateprincipally on the basis of electronic commands (a so-called“steer-by-wire” arrangement) and the steering column may in that caseneed to be long enough only to journal a steering wheel relative to thecab fascia or dashboard. The first and second servomechanisms may bemanufactured in such sizes and may be located on the steering column soas to accord with such a steering column design. The principal,operative part of a steering mechanism as defined below while referredto as a “steering column” may not be recognisable as such in theconventional sense; and need not be mounted relative to a fascia ordashboard as mentioned above. All such variations are within the scopeof the invention.

Moreover the steering set-up of the vehicle may include parts andsub-systems that do not in the literal sense form part of a steeringcolumn. To this end herein the term “steering mechanism” is intended toembrace all mechanically, electrically, electronically orelectro-mechanically connected arrangements that convert driver or othersteering inputs into the steering action of ground engaging members.

In a further optional refinement the vehicle of the invention mayinclude at least one receiver of transmitted vehicle guidance signalsand at least one controller that converts received guidance signals tosteering input commands that are input to the first steeringservomechanism and/or the second steering servomechanism.

As a result the vehicle of the invention may be arranged to operate inaccordance with a remote guidance regime.

As an example of such an arrangement on very large farms the directionalguidance of tractors may occur on the basis of command signalstransmitted from an orbiting satellite that in turn may contain storedwithin a memory device a map of the field in which a tractor operates.Such an automatically guided vehicle does not require the input of anoperator at all when performing field tasks, and instead manoeuvres independence on data transmitted from the satellite and received by thevehicle-mounted signal receiver.

An arrangement of this kind could operate on the basis of “GlobalPositioning System” signals, or other signals created specifically forthe farm in question.

Another example of use of a vehicle equipped with a signal receiverarises when performing operations such as ploughing or seeding in a verylarge field. In such a case if the field is of an essentially regularshape such as a rectangle a contractor may operate multiple tractorssimultaneously in the field. As a result it may be possible to completethe field task very quickly (and thereby for example take advantage offavourable meteorological conditions, or the scheduling of use of thevehicles in question).

Since each of the tractors will complete essentially the same manoeuvresas the others, albeit in each case following a line displaced to oneside or the other across the width of the field compared with anadjacent tractor, it is not necessary to provide a driver in the cab ofeach tractor. On the contrary it may be possible for only one, “command”tractor to be operated by a driver, and for the others in the group tobe driverless.

The command tractor may operate under the control of the driver or onsome other basis (such as an automated guidance regime) and may transmitguidance commands via a transmitter to the other vehicles in the group.The latter would receive the commands and generate control commands forone or both of the steering servomechanisms. As a result the driverlesstractors could for example copy the manoeuvres of the “command” tractor,or could replicate them in a modified way that takes account of thelateral displacement or localised conditions in the portion of the fieldin which the driverless vehicles operate.

In yet a further variant all the tractors in a group could be driverlessand could receive remotely generated guidance/steering commands. Asupervisor could oversee operations of the tractors of the group fromthe edge of the field, or even from a remote location (using e.g.telemetry equipment such as video cameras coupled to transmitters andfitted to one or more of the tractors).

Preferably the amount of steering assistance is adjustable depending onat least one of the following signals:

-   -   vehicle speed or wheel speed    -   steering wheel angle    -   electric motor position (angle)    -   joystick position    -   steerable wheel alignment angle    -   torque on the steering column    -   hydraulic pressure in one or more hydraulic steering cylinder(s)    -   driver input torque on the steering wheel    -   electric motor supply current or voltage    -   guidance signals.

When referring to the alignment angle of steerable wheels in thiscontext one may consider front steerable wheels (as are present in aconventional tractor); rear steerable wheels such as those commonlyemployed in a combine harvester; and/or an articulated vehicle framearrangement, as used in a so-called bi-directional or articulatedtractor, in which hydraulic cylinders cause articulation of front andrear parts of a vehicle frame. The invention is applicable to all suchtypes of steering set-up; and references herein to “steerable wheels”and similar components should be construed accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows a description of preferred embodiments of theinvention, by way of non-limiting example, with reference being made tothe accompanying drawings in which:

FIG. 1 is a schematic, perspective view of parts of a vehicle, accordingto the invention, embodying features as described herein;

FIG. 2 shows an example of a “human-machine interface” (HMI) that issuitable for use in a vehicle according to the invention;

FIG. 3 is a perspective view showing the HMI of FIG. 2 installed in thecab fascia of an agricultural tractor;

FIG. 4 is a perspective view showing the location in the cab of atractor according to the invention of some further components formingpart of the invention

FIG. 5a shows in plan view from above an example of a first manoeuvre(passing from a road into a field) that may be performed by a tractor,and FIG. 5b shows the status of the HMI of FIGS. 2 and 3 at such a time;

FIG. 6a shows an example of a second manoeuvre (carrying out a taskinvolving passing along the field) that may be performed by the tractorof FIGS. 5a and 5b , and FIG. 6b shows the prevailing status of the HMduring the manoeuvre;

FIGS. 7a and 7c show an example of a third manoeuvre (initiating andcompleting a headland turn) that may be performed by the tractor, andFIGS. 7b and 7d show the statuses of the HMI;

FIG. 8a shows an example of a fourth manoeuvre (returning from the fieldto a road) that the tractor may complete; and

FIG. 8b shows the status of the HMI at such a time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings a self-propelled vehicle in the form of atractor 20 (FIGS. 3-8) according to the invention includes a rotatablesteering column 21.

In the embodiment illustrated the steering column 21 takes the form ofan elongate rod that over the major part of its length is solid andrigid.

The steering column 21 in the preferred embodiment shown interconnectsat an upper end, inside the cab 22 of the tractor 20, a steering inputmember in the form of a conventional steering wheel 23 and at a lowerend, inside the powertrain compartment of the tractor at its forwardend, the control valve 24 of a hydraulic steering assistance sub-systemthat is described in more detail below.

In the majority of embodiments of the invention the steering wheel oranother steering input member would be present, but it is possible todevise driverless versions of the vehicle of the invention in which itwould not be strictly necessary to provide a steering input member. Inpractice however even in a version of the vehicle that is intended to bedriverless a steering input member typically would be present in orderto provide the option of driver-operation should this be desired.

The steering column 21 is journalled in one or more bearings at two ormore locations along its length in order to permit it to rotate aboutits longitudinal axis. The bearings are omitted from FIG. 1 for ease ofillustration, and may be of conventional designs.

The steering column 21 optionally may include any of a range ofengineering features that are commonplace in such components. Theseinclude collapsible sections that absorb energy in the event of a crashaccident, and articulated joints such as optional joint 42 that isvisible in FIG. 1 permitting the transfer of rotational motion in asteering column that is not completely straight along its whole length.

The tractor 20 includes in the embodiment shown four ground-engagingmembers in the form of pairs of front (26) and rear (27) wheels (FIG. 5a).

The front wheels 26 are steerable as a result of rotation of thesteering column 21. To this end the steering column 21 is operativelyconnected at its forwardmost end 21 a to a series of steering linkagemembers that constitute a steering mechanism.

The steering mechanism interconnects the steering column 21 and thefront, steerable wheels 26 in a manner that converts rotational movementof the steering column 21 into rotations of the essentially uprightwheels 26 about the caster (steering) axis that is a well knownparameter of steerable wheel design.

The vehicle 20 of the invention includes a first steering servomechanismin the form of the hydraulic steering assistance sub-system mentionedabove.

This sub-system includes the hydraulic control valve 24 that in thepreferred embodiment of the invention is a double acting, bidirectionalproportional valve having a rotary input to which the lowermost end 21 aof the steering column 21 is secured such that rotation of the steeringcolumn 21 clockwise and anti-clockwise causes movement of e.g. a valvespool to either side of a centre (closed) position.

The valve 24 includes connected thereto in a per se known manner on aninput side a pair of hydraulic feed lines 28, 29 that are in turnconnected to output ports of a pump for pressurising hydraulic fluid(e.g. oil) in the circuit constituted by the valve 24 and relatedcomponents.

On an output side valve 24 connects by way of further hydraulic feedlines 31, 32 to a double acting, hydraulic cylinder 33.

Cylinder 33 is as illustrated mounted securely in the vehicle 20 in anorientation that under normal use of the vehicle is horizontal. At eachend the cylinder 33 includes a respective extensible steering linkagearm 34, 36.

Each of the linkage arms 34, 36 terminates at a free end in a rose joint37 or a similar fixing by which it secures to the stub axle of one ofthe steerable front wheels 26.

Rotation of the steering column as stated moves the spool of valve 24away from its centre position. This pilots pressurised hydraulic oil fedinto the valve 24 via the lines 28, 29 in a manner causing simultaneousextension of one of the linkage arms 34, 36 outwardly from the cylinder33 and retraction of the other to a location withdrawn inside thecylinder 33. This causes power-operated steering of the wheels 26 tooccur, in a manner that is known per se.

The hydraulic steering assistance sub-system illustrated additionallyincludes return hydraulic fluid line 38 that interconnects the valve 24and the pump for the purpose of recirculating hydraulic oil expelledfrom the cylinder 33 as a result of retraction of one or other of thelinkage arms 34, 36.

As described above in the event of the first steering servomechanismceasing to provide assistance the cylinder 33 in effect becomes a rigidtransverse steering linkage member by reason of the trapping of a columnof hydraulic fluid inside it. The cylinder therefore may transferrotations of the steering column as steering movements of the wheels 26even if e.g. the hydraulic fluid pump ceases operating.

The vehicle 20 of the invention also includes a second steeringservomechanism in the form of an electric steering assistance sub-systemconstituted by a steering column rotary electric motor 39 and acontroller in the form of an electronic control unit (ECU) 41.

The electric motor 39 in the embodiment shown is mounted with its axisof rotation extending transversely of the steering column 21. A pinionor other drive-transferring gear at the end of the output shaft of themotor engages a similar pinion that is connected to the steering column21. Powered rotation of the output shaft causes powered assistance ofthe rotation of the steering column 21 in a per se known manner. Thetorque and the extent of rotation of the motor 39 are controlled independence on control commands generated in the ECU 41, that isoperatively connected to the motor 39 e.g. by way of a CAN-BUS formingpart of the control system of the tractor 20, or by any equivalentmeans.

The nature of the coupling between the output shaft of the motor 39 andthe steering column 21 is such that in the event of the motor offeringno assistance (for example if there is a component failure in the secondsteering servomechanism) rotation of the steering column 21 as a resultof rotation of the steering wheel alone is not prevented.

The two servomechanisms described are associated with differingcharacteristics in terms of the steering assistance they provide.

Thus for example the hydraulic valve 24 and cylinder 33 amount to aso-called “non reactive” assistance sub-system. By this is meant anarrangement in which the assistance force may be maintained at the samevalue regardless of the degree to which the steering wheel 23 is turned.

This means that considered on its own the first steering servomechanismof the vehicle of the invention does not provide any self-centringeffect and instead is useful to maintain a constant steering angle. Thusin situations in which it is desired to steer a steady curvecontinuously with little or no driver input the controller (ECU) 41 ofthe invention may operate so that a relatively large proportion of thesteering assistance power is provided by the hydraulic circuitconstituting the first servomechanism, and a relatively small proportionby the second, electric servomechanism.

Similarly the first servomechanism described can provide a significantdamping effect in the steering response of the vehicle (the degree ofdamping being inversely proportional to the tendency of the steering tobe deflected e.g. by undulations in the surface on which the vehicletravels). Therefore when travelling in straight lines (for example whenploughing or sowing) again it may be desirable for the controller toensure that a relatively large proportion of the assistance is providedby the hydraulic circuit constituting the first steering servomechanism.

It is possible to achieve a relatively low, or zero, proportion ofassistance from the second, electric steering servomechanism by reducingthe current supplied to the motor 39 in dependence on the signalsgenerated in the controller (ECU) 41.

In other circumstances, such as when moving on roads, it may bepreferable to increase the assistance provided by the second, electricsteering servomechanism. It may be possible to devise embodiments of theinvention in which adjustment of the relative amounts of steeringassistance provided respectively by the first and second servomechanismsoccurs by reducing the pump pressure seen at the actuator 33. In thepreferred embodiments of the invention tested however the assistanceprovided by the first, hydraulic servomechanism remains constant whilethe amount of assistance provided by the second, electric servomechanismis adjusted as stated in order to produce the desired effects.

At yet other times it may be desirable to operate with maximalassistance provided by both the servomechanisms, such as when wishing toconvert quickly from full right steering lock to full left steering lock(or vice versa).

Examples of some modes of assistance that are as a result possibleinclude but are not limited to the following:

“Effortless” sub-mode: the electric motor 39 (first servomechanism)provides a torque that almost exactly compensates the friction forces onthe steering column. Therefore with a very low input force requirement(or even zero or almost zero if desired) the driver can steer thevehicle.

“Lock-to-lock” sub mode: the driver provides an initial rotary forceinput motion to the steering wheel 23, and thereafter does not need toprovide any further torque input. The electric motor 39 moves the frontwheels until the lock position is reached at the constant speed given bythe driver. The assistance interrupts immediately in the event of thedriver again grasping the steering wheel.

“Go to centre mode”: This is similar to the “lock-to-lock” sub-mode, butthe front wheel alignment stops adjusting when the wheels reach adesignated centre position.

Desirably therefore the vehicle 20 of the invention includes a means forselecting the degree of assistance offered by at least one of theservomechanisms (i.e. preferably the second, electric servomechanism)between a minimum level (that might represent no assistance at all,depending on the precise design of the vehicle and the servomechanisms)and a maximum representing a safe performance limit of theservomechanism.

One form that such a means may take is the human-machine interface (HMI)panel 43 shown in FIGS. 2, 3 and 5 b-8 b.

The HMI panel 43 may be of a wide variety of possible designs. The basicfunctions of the panel 43 are:

-   -   selection of the steering assistance depending on the work        condition (headland, field, road, etc.)    -   selection of transition mode between different assistance levels        (i.e. manual, related to the HTS (headland turning sequence)        button; other vehicle functions; automatic)

The HMI by which selection of modes of operation, such as but notlimited to those outlined above, may be made as stated can take avariety of forms. One desirable characteristic of such a panel whenemployed in an agricultural vehicle such as a tractor is that it isquick and simple to use. This is primarily for the reasons given above,namely that a tractor driver often must respond quickly torapidly-changing circumstances while operating complicated sub-systemsof a heavy, powerful vehicle. Simplicity and speed of operationtherefore are often very important in the design of tractor sub-systems.

Also a tractor driver may have to work wearing gloves or otherprotective clothing that limits his dexterity. Ideally the panel 43should be designed with such features in mind.

Different requirements however may arise in other types of vehicle, andfor this reason among others the HMI panel 43 described herein is merelyexemplary and is not limiting of the scope of the invention.

HMI panel 43 includes a pair of mode selection buttons 44, 46 that ifdesired may be secured in an accessory panel 47. Each button 44, 46 liesadjacent an array of sub-mode indicator lamps 44 a, 44 b, 44 c, 44 d, 46a, 46 b, 46 c, and beneath each button 44, 46 on the panel 47 is markeda respective legend indicating the circumstances under which aparticular menu of steering assistance modes should be selected.

The legends shown are suitable for use in an agricultural tractor, andtherefore read “HEADLAND” adjacent button 44 (which therefore is used toselect steering assistance modes suitable for tractor turns in fieldheadlands) and “FIELD/ROAD” adjacent button 46 (which therefore selectsmodes appropriate to driving on relatively smooth surfaces and/or whenthere is little need for significant turn assistance).

Each of the buttons is wired and/or is connected to ECU 41 such thatpressing of one button 44, 46 automatically cancels any prevailingselection made using the other button. Each sequential press of one ofthe buttons causes the selection of the sub-modes indicated by theadjacent array of indicator lamps 44 a-d or 46 a-c in turn, such thatthe mode selection buttons may be used to “scroll” through the sequenceof sub-modes until a desired sub-mode is selected.

The sub-mode indicator lamp of a selected sub-mode illuminates asselection occurs. An appropriate legend identifying each mode, asillustrated in FIG. 2, is marked adjacent each respective indicatorlamp.

In addition to the foregoing, as described in more detail below, theselection of at least some modes may take place on an automatic basis.

FIG. 3 shows location of the HMI 43 of FIG. 2 in one exemplary positionin the front dashboard 48 inside the cab 22 of a tractor 20. Otherlayouts and positions are of course possible within the scope of theinvention and will vary from one design of vehicle to another.

FIG. 4 further illustrates one way, of many, in which certain componentsas described herein may be located in the vehicle cab 22.

FIG. 4 shows a vehicle steering wheel 23 in a conventional location. Ashroud that normally obscures the parts of the steering column 21 thatlie inside the cab 22 has been removed to show one possible location forthe motor 39 forming part of the second steering servomechanism.

Also visible in FIG. 4 is a joystick 49 that is provided in certaintractor designs in order to provide control for various functions of thetractor 20.

The joystick is a second driver-operated steering input member that iselectronically coupled and is configurable (e.g. as a result of pressingof an actuation button) to act as an input member via which the tractoroperator may input steering commands.

The joystick is useful in particular when the vehicle operator isperforming manoeuvres requiring him/her to look out of the rear window51 of the cab 22. Controlling the steering of the tractor 20 isconsiderably easier at such a time when the joystick is used instead ofthe steering wheel 23. In some tractors 20 an operator's seat 52 iscapable of swivelling to make it comfortable for the operator to controlthe tractor 20 while looking out of the rear window 51.

Referring now to FIGS. 5-8 a number of options are illustrated forselecting the sub-modes that are available in the exemplary tractor 20described above. As indicated elsewhere herein, the list of sub-modesdescribed and their grouping as sequences are not intended to belimiting of the invention, and many other combinations of sub-modes ofsteering control are possible.

In FIG. 5a the tractor 20 is shown travelling on a relatively smoothroad surface 53 just before turning in to a field 54 via a field gateway56 that marks a transition from one type of operation (driving on road)to another (e.g. spreading, spraying, seeding, ploughing, harrowing,rolling or otherwise treating the soil of the field).

While driving on the road the operator of the tractor 20 selects the“FIELD/ROAD” menu of sub-modes by pressing button 46 of HMI 43 assignified in FIG. 5 b.

In the illustrated embodiment of the invention this results in theselection of the sub-mode “Transport” that is signified by illuminationof indicator lamp 46 a.

The “Transport” sub-mode applies steering assistance, using the firstand second steering servomechanisms under control of the ECU 41, suchthat the steering is reactive and self-centring. The aim of the“Transport” sub-mode is to replicate as far as possible in a tractorweighing several tonnes the feeling of steering a passenger car on theroad 53. This assists the tractor operator to respond to road situationsin a similar manner to the other road users nearby.

Selection of one sub-mode via the HMI 43 inhibits the selection of allother sub-modes, that would as a result need to be selected specificallyin order to take effect.

However in the preferred embodiment shown selection of “Transport” modein particular may occur automatically when the tractor 20 moves on aroad. Automatic selection of “Transport” mode may take place for examplewhenever the forward speed of the tractor exceeds a chosen threshold(such as but not limited to 25 km/h) signifying on-road driving. The ECU41, that preferably is programmable, may include an algorithm thatachieves this effect.

Once the tractor 20 is in the field 54 the operator may as desired usethe mode selection button 46 as many times as desired in order to“scroll” the menu of available sub-modes and select the one that mostaccurately suits the field conditions and the tasks that the tractormust fulfil.

Thus the operator may maintain the selection of the “Transport” sub-mode(for example if the field is relatively smooth and flat, as is often thecase in certain types of livestock pasture and fields that arecultivated for forage growing), or he/she may select a “Damp” sub-mode(in which damping of the steering as explained herein is at a maximallevel) or an “Effortless” sub-mode in which the effort to rotate thesteering wheel is very low, or perhaps even zero.

The “Damp” sub-mode as indicated is particularly suitable when operatingin rutted or furrowed ground in which it would otherwise require veryconsiderable effort on the part of the operator to make the tractor 20maintain a chosen course. Also the “Damp” mode would be suitable if itwas necessary to follow a continuously curved course, representing forexample a curved field margin.

The effortless sub-mode is suitable for making headland operationsfaster than would otherwise be the case and with a lower effort requiredon the part of the vehicle operator.

FIG. 6b shows the “Damp” sub-mode button 46 b illuminated by way ofillustration.

While performing operations in a field the operator may in additionselect a further operational mode, in which the joystick 49 if fitted tothe tractor 20 becomes active as the steering input member. In theillustrative embodiment described selection of this mode may take placethrough depressing of a button on the joystick 49 itself, but in otherembodiments alternative ways of selecting the sub-mode may be available.Examples include but are not limited to use of one or a combination ofthe mode selection buttons 44, 46 or another button that may also formpart of the HMI. Selection of a reverse gear or the activation of arear-mounted implement may also be used to initiate steering input viathe joystick 49.

In FIG. 7a the tractor 20 has temporarily ceased field operations inorder to permit turning in a headland 57 at an end of the field 54.

Normally in the headland any implement or other ground-treatingaccessory of the tractor 20 is deactivated (e.g. by raising of theimplement out of engagement with the soil, by closing off seed coulters,by switching off spray pumps and so on). The requirement of the tractoroften then becomes one of maximum manoeuvrability in order to allow itto turn as smoothly, safely and quickly as possible in the headlandmargin.

When entering a headland therefore the operator of the tractor 20 maypress the “HEADLAND” mode selection button 44 that in the embodimentshown would result in selection of the first of the headland sub-modes(i.e. “Damp” in the illustrated example).

The “Damp” sub-mode available via the HEADLAND menu may be the same asthe “Damp” sub-mode available through pressing the “FIELD/ROAD” modeselection button, or it may result in the operation of a differentprogramme that causes different combinations of the damping effectsavailable from the two steering servomechanisms.

The operator may also select an “Effortless” sub-mode in which thesteering becomes as light as possible (i.e. maximum assistance isprovided using the two steering servomechanisms); a “Back to centre”sub-mode, in which the self-centring is maximised; and a “Lock-to-lock”mode in which movement of the steering wheel when at one extreme ofsteering lock causes assisted rotation to the opposite lock setting.This last mentioned mode may be of help for example when the headland isparticularly confined.

FIG. 7b shows the “Effortless” sub-mode indicator lamp in an illuminatedstate, signifying selection of that sub-mode.

In some tractors and other agricultural vehicles the electronics and/orthe software are programmable for the purpose of recording a sequence ofcontrol actions. One example of when this is beneficial is whenperforming a turn in the headland of an essentially rectangular fieldduring operations that rely on use of an implement.

On the occasion of a first turn of this kind that the vehicle makesafter entering such a field the tractor operator may press a “PROGRAM”or “RECORD” button before carrying out the headland turn steps (i.e.raising the implement attached to the tractor, selecting a chosen lowgear ratio, adjusting the engine governor and operating the steeringwheel to perform the turn before re-engaging the implement and selectingthe appropriate gear and governor settings for continuing field work).Pressing of the PROGRAM or RECORD button (assuming one is present)causes the vehicle control software to store the sequence of steps sothat the headland turns may be reliably performed each time the vehiclereaches an end of the field.

The apparatus and operation of the invention are compatible with such anarrangement and indeed the selection of particular modes and sub-modesas described above may if desired be treated as recordable steps thatcan form part of a sequence as described above.

FIG. 7c illustrates the tractor 20 resuming field operations aftercompletion of a headland turn. In the preferred embodiment of theinvention the tractor operator presses the “FIELD/ROAD” button in orderto effect a transition back to the same sub-mode of assistance thatprevailed before initiation of the headland turn. Thus in FIG. 7d the“Damp” sub-mode indicator lamp 46 b is illuminated. This lamp 46 b alsomay be arranged to flash during the headland turn in order to remind theoperator of the sub-mode to which the tractor steering would returnfollowing pressing of the mode selection button 46 at the end of theturn.

FIG. 8a shows the tractor leaving the field 54 and returning to the road53 at the end of a period of work. The operator may select the“Transport” sub-mode using the button 46 at this time; or he/she maysimply permit automatic selection of this mode to occur as the forwardspeed of the tractor exceeds the chosen threshold value.

In addition to the foregoing modes, as explained the tractor 20 may beequipped with a so-called “autoguidance” device (such as a GlobalPositioning System receiver, or another type of receiver of steeringand/or navigation signals). Also as explained above such signals mayderive from satellites in Earth orbit, other vehicles (such as othertractors working nearby) or even fixed transmitters. When so equippedthe tractor 20 may manoeuvre without need for operation of the steeringinput devices such as steering wheel 23 or joystick 49. Such devicestherefore may be dispensed with, although preferably at least thesteering wheel 23 would be retained.

The listing or discussion of an apparently prior-published document inthis specification should not necessarily be taken as an acknowledgementthat the document is part of the state of the art or is common generalknowledge.

The invention claimed is:
 1. A steerable, self-propelled vehicleincluding an agricultural tractor, the steerable self-propelled vehiclecomprising: a steering mechanism having a rotatable steering column thatis connected to control a steering angle of one or more ground-engagingmembers of the vehicle, the vehicle including a first steeringservomechanism acting on the steering mechanism in a first location, thefirst steering servomechanism including a hydraulic steeringservomechanism including a hydraulic steering valve that generates apilot hydraulic signal in relation to the rotational angle of thesteering column and at least one hydraulic steering cylinder connectedto adjust the steering angle of the one or more ground-engaging members,the pilot hydraulic signal being piloted to control the hydraulicsteering cylinder, the first steering servomechanism having at least afirst steering assistance characteristic; a second steeringservomechanism acting on the steering mechanism in a second location,the second steering servomechanism including an electric power steeringservomechanism including a motor for generating a torque that acts onthe steering column, and a signal generator for generating controlsignals determining the magnitude and direction of action of the torque,the second servo mechanism having a second steering assistancecharacteristic; and a programmable controller for causing the first andsecond steering assistance characteristics to influence the steering ofthe vehicle in dependence on one or more control commands generated inthe controller, wherein the vehicle includes a human-machine interface(HMI) using which a driver may input commands selecting two or moreprogrammed modes of operation of the steering servomechanisms, whereinthe HMI includes switching interfaces for selecting between programmedmodes that control steering during movement of the tractor respectivelyin a field headland and in other locations, wherein the HMI includesrespective switches for selecting the programmed modes and sequentiallyselecting sub-modes following selection of a said programmed mode, andwherein the sub-modes available following selection of headlandoperation include a damped steering sub-mode, a maximal assistancesub-mode, an automatic steering centring sub-mode, and a lock-to-lockassistance sub-mode, and the sub-modes available following selection ofother location operation include an on-road sub-mode, a damped steeringsub-mode, and a maximal assistance sub-mode.
 2. A steerable,self-propelled vehicle according to claim 1 that is driver-operated andincludes one or more steering input members operatively connected to thesteering column, wherein the controller generates control commands independence on one or more driver inputs via at least one steering inputmember.
 3. A steerable, self-propelled vehicle according to claim 1wherein the other locations include fields and roads.
 4. A steerable,self-propelled vehicle according to claim 1 including two or moreselectively operable steering input members connected to the steeringcolumn that include a steering wheel and a joystick.
 5. A steerable,self-propelled vehicle according to claim 4 wherein the steering wheelis mechanically coupled to the steering column.
 6. A steerable,self-propelled vehicle according to claim 4 wherein the joystick iselectronically coupled to the second steering servomechanism.
 7. Asteerable, self-propelled vehicle according to claim 1 including atleast one receiver of transmitted vehicle guidance signals and at leastone controller that converts received guidance signals to steering inputcommands that are input to the first steering servomechanism and/or thesecond steering servomechanism.
 8. A steerable, self-propelled vehicleaccording to claim 1 wherein the amount of steering assistance isadjustable depending on at least one of the following signals: vehiclespeed or wheel speed; steering wheel angle; electric motor position;joystick position; steerable wheel alignment angle; torque on thesteering column; hydraulic pressure in one or more hydraulic steeringcylinder(s); driver input torque on the steering wheel; electric motorsupply current or voltage.